Study On The Application Of Modified Lithium Phosphate Catalyst In The Propylene Oxide Isomerization

Allyl alcohol has been widely used as the basic chemical raw material,mainly because its molecular structure has two functional groups,including double bond and hydroxy,which can participate in oxidation,reduction,etherification,esterification and other reactions.At present,the common preparing method of allyl alcohol is gas phase propylene oxide isomerization,which is simple process,high efficiency and little pollution.The catalytic activity and selectivity of basic lithium phosphate catalyst for propylene oxide isomerization are high.But the catalyst is easy to carbon deposition and inactivation.It is difficult to the continuous production.In view of the above problems,in this paper,the steam treatment and the gold loading of the catalyst were used to inhibit the formation of carbon deposition and enhance the activity of the catalyst.In order to find a more suitable catalyst for the propylene oxide isomerization,a variety of catalysts were studied.The steam treatment of the catalyst obviously inhibited the surface carbon deposition of the basic lithium phosphate catalyst.And the catalytic activity was also obviously improved.The results showed that the catalyst which was pre-treated with steam at 300 ? for 30 minutes exhibited excellent catalytic activity.Furthermore,the amount of carbon deposition was 15.1%,much lower than that of the untreated catalyst?21.5%?.The decrease of the amount of Bronsted acid sites resulted in the reduction of carbon deposition.The enhancement of activity could be attributed to the increase of synergistic sites,and this could be due to an increase in the amount of Lewis acid sites and in the strength of the base sites.The Au/Li₃PO₄ catalyst was prepared,and the catalytic activity of lithium phosphate was obviously improved.The experimental results showed that the Au/Li₃PO₄-13 catalyst with gold loading content of 0.042 wt%which was calcined at 300 ? showed the best performance.Moreover,the experimental results showed that the increase of catalytic activity might be due to the enhanced strong basic strength of supported catalyst.In addition,XPS spectra and density functional theory were employed to verify that the charge transfer from oxygen species to gold species led to the electron-rich gold species which acted as stronger base sites.In order to find a more suitable catalyst,all kinds of catalysts were studied.The experimental results showed that Ag and Cu can not improve the catalytic activity of lithium phosphate.On the contrary,they might inhibit the catalytic activity of lithium phosphate.As for TiO2,zeolite X catalyst,g-C3N4,Au-Pd/TS-1,solid superacid,nano-Ag,CeO2-TiO2 catalysts,the conversion of propylene oxide was below 10%.But the selectivity of propyl aldehyde was almost 50%.Compared with the lithium phosphate catalyst,these catalysts exhibited higher selectivity of propyl aldehyde.Therefore,after the modification of the catalyst,these catalysts might be suitable to the propylene oxide isomerization to get propyl aldehyde.This part of the work remains to be further studied.